In the area of building and construction, concrete wall panels have been fabricated and then coated or layered with insulation having relatively low strength to provide a well-insulated wall structure having high strength. Typically, a structural wall is built and insulation is applied when finishing the wall. The insulation inhibits the flow of thermal energy through the wall.
A commonly used measurement of the thermal insulating qualities of a material is the mathematical coefficient “R”, which is a measure of the thermal resistance of a material. The coefficient R is equal to the thickness divided by the thermal coefficient “K”. A high R value provides a high degree of high thermal resistance or insulating ability.
Concrete, formed of hydraulic cement binder, water and aggregate is a relatively high strength, low cost building material. Unfortunately, concrete has the drawback of offering a poor K value and thus provides little thermal insulation. An 8 inch slab of concrete has an R value of approximately 0.64; a 1 inch panel of polystyrene foam has an R value of approximately 5; and a 3.5 inch layer of glass fiber building insulation provides an R value of approximately 13. Polystyrene and fiberglass provide a high R value but offer little or no structural strength.
Often walls are built with a structural layer that has a decorative wythe fixed to the outer or inner surface. The wythes typically include an intermediate space that can be fitted or retrofitted with any number of insulating materials, including fiberglass or polystyrene foams. The R-value of two insulated wythe walls is limited due to the structural bridging between the outer and inner wall. The structural bridging provides high strength and integrity and prevents the walls from collapsing. Structural bridges are typically metal studs, bolts, or beams. The structural bridges also serve as thermal bridges because the metal allows a thermal short bypassing the insulation. These thermal bridges cause the R-value of the constructed wall to be substantially lower than the R-value of the insulation wythe. U.S. Pat. No. 4,393,635 to Long, U.S. Pat. No. 4,329,821 to Long et al., U.S. Pat. No. 2,775,018 to McLaughlin, U.S. Pat. No. 2,645,929 to Jones, and U.S. Pat. No. 2,412,744 to Nelson disclose wall structures held together using metal tie rods or studs.
U.S. Pat. No. 4,829,733 to Long provides a plastic tie for forming an insulated wall having inner and outer concrete structural wythes with highly insulating wythes therebetween. The plastic tie is used in the construction industry, but is relatively expensive and difficult to manufacture and does not provide adequate composite action.
Composite action describes how well a multi-layered panel, or composite wall, transfers shear forces between its different wythes and is typically identified as a percentage between 0% and 100%. High composite action results in the transfer shear forces between the structural wythes so that the composite wall will have a moment of inertia approaching that of a solid wall having the overall thickness of a three wythe wall. Low composite action does not transfer shear forces and the wall will have a moment of inertia approaching that of the sum of moments of inertia of the individual wythes. Composite action provides structural integrity to the wall. Composite action is highly desirable because it strengthens the wall against the forces of the wind and reduces deflection of the wall. A high composite action wall can also be designed to meet code requirements while reducing the mass and cost of the wall. Accordingly, it is generally desirable to produce composite walls having high composite action so that they will remain intact when loads are applied to a wall. Existing connectors, however, have thus far proven inadequate for providing composite walls with the desired composite action. Although Composite Technologies Corporation, the assignee of the Long '733 patent, has made the claim that some of its connectors are able to provide 40% to 60% composite action, independent testing has shown that such connectors only provide about 10% composite action.
Insulated walls generally include an insulation wythe sandwiched between a structural wythe and a fascia wythe. The structural wythe is typically used as the load-bearing member of the wall. The fascia wythe is typically not used to bear a load separated from the structural wythe because of insufficient composite action existing between the facia wythe and the structural wythe. However, if the composite action of the wall was sufficiently high, e.g., between 60% to 100%, the fascia wythe could potentially be used to bear a substantial portion of the overall load.
Accordingly, there is currently a need in the art for insulating composite walls with high composite action.